Traditional manufacturing techniques for assembling components to produce large mechanical structures to a specified contour traditionally have relied on fixtured tooling techniques utilizing floor assembly jigs and templates to locate and temporarily fasten detailed structural parts together to locate the parts correctly relative to one another. This traditional tooling concept usually requires at least one primary assembly tool for each subassembly produced, and movement of the parts from tool to tool for manufacturing operations as they are built up.
The tooling is intended to accurately reflect the original engineering design of the product, but there are many steps between the original design of the product and the final manufacture of the tool. It is not unusual that the tool as finally manufactured produces parts that are outside of the dimensional tolerances of the original part design, and, more seriously, the tool can become out of tolerance from typical hard use it receives in the factory. Moreover, dimensional variations caused by temperature changes in the factory can produce a variation in the final part dimensions as produced on the tool. Also, hand drilling of the part on the tool produce holes that are not perfectly round when the drill is presented to the part at a slightly nonperpendicular angle to the part, and also when the drill is plunged into the part with a motion that is not perfectly linear. Parts can shift out of their intended position when they are riveted in non-round holes, and the non uniform hole-to-rivet interference in a non-round hole lacks the strength and fatigue durability of round holes. The tolerance buildup on the part as it is moved from tool to tool can result in significant deviation from the original design dimensions, particularly when the part is located on the tool at one end of the part, forseeing all of the part variation in one direction instead of centering it over the true intended position. Finally, this traditional hard tooling is expensive, difficult to change when design changes are implemented and takes up a large amount of factory floor space.
These disadvantages of the use of hard tooling are inherent in the concept and, although they can be minimized by rigorous quality control techniques, they will always be present to some extent in the manufacture of large mechanical structures using hard tooling.